我写了一个程序,以从12点钟方向开始顺时针排列图表上的点,使包含这些点的向量按照该顺序排序。我使用 atan2 来获取相对于 12 点钟方向的角度,然后根据象限进行调整。我正在尝试找出 bug 来源,因为它没有正确地对它们进行排序。因此,给定4个类似照片中的随机点,它应该按照在图片中展示的规则将它们排序为 P1、P2、P3、P4。
以下是我的代码:
//sort_points.cpp
#include <iostream>
#include <math.h>
#include <algorithm>
#include <vector>
using namespace std;
class Point
{
public:
double x;
double y;
Point(double xx, double yy) : x(xx), y(yy) {}
~Point();
inline friend ostream& operator<<(ostream& output, const Point& point)
{
output << "[" << point.x << ", " << point.y <<"]";
return output;
}
};
Point::~Point() {;}
/* get quadrant from 12 o'clock*/
int get_quadrant (const Point& p)
{
int result = 4; //origin
if (p.x > 0 && p.y > 0)
return 1;
else if(p.x < 0 && p.y > 0)
return 2;
else if(p.x < 0 && p.y < 0)
return 3;
//else 4th quadrant
return result;
}
double get_clockwise_angle(const Point& p)
{
double angle = 0.0;
int quadrant = get_quadrant(p);
/*making sure the quadrants are correct*/
cout << "Point: " << p << " is on the " << quadrant << " quadrant" << endl;
/*add the appropriate pi/2 value based on the quadrant. (one of 0, pi/2, pi, 3pi/2)*/
switch(quadrant)
{
case 1:
angle = atan2(p.x,p.y) * 180/M_PI;
break;
case 2:
angle = atan2(p.y, p.x)* 180/M_PI;
angle += M_PI/2;
break;
case 3:
angle = atan2(p.x,p.y)* 180/M_PI;
angle += M_PI;
break;
case 4:
angle = atan2(p.y, p.x)* 180/M_PI;
angle += 3*M_PI/2;
break;
}
return angle;
}
bool compare_points(const Point& a, const Point& b)
{
return (get_clockwise_angle(a) < get_clockwise_angle(b));
}
int main(int argc, char const *argv[])
{
std::vector <Point> points;
points.push_back( Point( 1, 3 ) );
points.push_back( Point( 2, 1 ) );
points.push_back( Point( -3, 2 ) );
points.push_back( Point( -1, -1 ) );
cout << "\nBefore sorting" << endl;
for (int i = 0; i < points.size(); ++i)
{
cout << points.at(i) << endl;
}
std::sort(points.begin(), points.end(),compare_points);
cout << "\nAfter sorting" << endl;
for (int i = 0; i < points.size(); ++i)
{
cout << points.at(i) << endl;
}
return 0;
}
atan2
函数返回从 3 点钟方向开始逆时针旋转的角度。 - qxz